136 



THE GEOLOGIST. 



These ova are deposited, according to M. 

 Guerin-Meneville, by Hemipteroiis (Xoto- 

 nectid) insects; the most abundant being the 

 Corixa femorata ; the other (which lavs the 

 larger eggs) being the Notonecta unifasciata. 

 They are said to fly about the water in my- 

 riads, and occasionally plunge below the sur- 

 face to the depth of several feet, there de- 

 positing the eggs. The Indians collect the 

 eggs, by placing bundles of reeds in the 

 water, which in twelve or fifteen days get 

 covered with millions of ova ; these they dry 

 for an hour or two, and remove from the 

 rushes, and sell as an article of food.* 



M. Yirlet d'Aoust remarks that probably 

 an analogous origin of oolite has existed in 

 all geological epochs ; and he points out 

 some of the conditions of certain oolites 

 that favour this view, — indeed, he seems to 

 think that nearly, if not quite, all oolites, 

 calcareous and ferruginous, have been formed 

 in this way.f 



The oolitic travertine of Tezcuco is also 

 described by Mr. E. B. Tylor, in the inte- 

 resting narrative of his travels in Mexico, 

 entitled ' Anahuac ; or, Mexico and the 

 Mexicans, Ancient and Modern,' 1859, al- 

 ready reviewed in the ' Geologist.' At page 

 156, he says : — 



" When I look through my notes about 

 Tezcuco, I do not find much more to men- 

 tion, except that a favourite dish here con- 

 sists of flies' eggs fried. These eggs are de- 

 posited at the edge of the lake, and the In- 

 dians fish them out and sell them in the 

 market-place. So large is the quantity of 

 these eggs, that at a spot where a little 

 streani deposits carbonate of lime, a pecu- 

 liar kind of travertine is forming, which t,. ^ ^. . 

 consists of masses of them imbedded 3n 



calcareous deposit. The flies which pro- tin^s, showing long linear ver- 

 duce tliese eggs are called by the Mexicans tical holes {b, c\, in section ; a 

 * axayacatl,' or ' water-face.' There was a surface. (Nat. size.) 

 cdebrated Aztec king who was called Axayacatl ; and his name is in- 

 dicated iu the picture-writings by a drawing of a man's face covered 



* M. Virlet d'Aoust gives much interesting information about this substance (termed 

 I aonll), ui the cuhnary and autiquarian points of view. See also a notice by :M. Gueriu- 

 MnieviUc, translated in the ' Annals of Nat. Hist.,' scr. 3, vol. ii p 313 



t Sec also, 'Geologist,' Vol. II. p. 73. 



